(a) Field of the Invention
The present invention is concerned with a digital function-of-time generator for digitally generating a function of time, and more particularly, it relates to a digital function-of-time generator which is quite suitable for use in imparting to a musical wave an envelope characteristic, such as attack and decay, in a digital electronic musical instrument.
(B) Description of the Prior Art
In electronic musical instruments in general such as electronic organs, arrangement is provided so as to impart the generated musical tones with transient effects such as attack and decay, i.e. the so-called tone envelope characteristic, by multiplying a musical tone waveshape having a constant amplitude which is generated from the tone generator section, by a function of time.
An example of such function generator designed to generate a function-of-time signal is shown in a Japanese periodical NIKKEI ELECTRONICS June 16, 1975, pages 84-107, entitled DIGITAL ELECTRONIC ORGAN. This known function generator, however, deals with an analog structure and cannot be termed as being an optimum arrangement for use as the component of a digitalized electronic musical instrument.
Also, an example of a function-of-time generator having a semi-digital structure is proposed in the specification of U.S. Pat. No. 3,819,844 to Sigeki ISII issued on June 25, 1974 under the title "ELECTRONIC MUSICAL INSTRUMENT KEYING SYSTEM WITH ENVELOPE SAMPLE MEMORIZING VOLTAGE DIVIDERS". This function generator stated in said U.S. application includes an envelope memory which stores a specific information (sample values) constituting a function (wave shape). This function-of-time generator is arranged to have a simplified structure to be operative so that this envelope memory is scanned to read out the stored function of time. However, the function-of-time generator itself is not digitalized fully. In addition, the time function which this function-of-time generator can generate is limited to those time functions which have been already stored in the envelope memory.